This application claims the priority of European patent application 02007292.2, filed Apr. 3, 2002, the disclosure of which is incorporated herein by reference in its entirety.
The invention relates to a flow sensor having a semiconductor chip with an integrated detector as well as to a method for producing the same. It also relates to a substrate to be used as semiconductor chip in such a sensor.
WO 01/84087 describes a flow sensor comprising a tube for the fluid to be measured and a semiconductor chip having a heat source and two temperature sensors. In one embodiment, gold or copper metal bumps are placed on the heat source and the temperature sensors. The chip is placed with the bumps against the tube and glued thereto. The gold and metal bumps provide a thermal connection between the tube surface and the heat source and temperature sensors, respectively.
Hence, it is a general object of the invention to provide a method, a sensor and a substrate of the type mentioned above that allow efficient production.
Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method comprises the steps of
providing a tube for containing a fluid to be measured,
providing a substrate with a flow detector integrated thereon, said flow detector having at least one heat source and at least one temperature sensor,
applying solder bumps to said heat source and said temperature sensor and/or to said tube,
placing said substrate against said tube and applying heat for melting said solder bumps, such that, after cooling, said solder bumps form a first thermal connection between said heat source and said tube and a second thermal connection between said temperature sensor and said tube, wherein the thermal connections are located at a distance from each other.
In a further aspect the invention relates to a method for producing a flow sensor, said sensor comprising a tube for containing a fluid to be measured and a substrate with at least one flow detector arranged thereon, said flow detector having at least one heat source and at least one temperature sensor, said method comprising the steps of
applying solder bumps to said heat source and said temperature sensor and/or to said tube,
attaching said substrate to said tube using flip chip technology by melting said solder bumps, such that, after cooling, said solder bumps form a first thermal connection between said heat source and said tube and a second thermal connection between said temperature sensor and said tube, wherein the thermal connections are located at a distance from each other.
In yet another aspect, the invention relates to a flow sensor comprising
a tube for containing a fluid to be measured,
a semiconductor substrate with a flow detector integrated thereon, said flow detector having at least one heat source and at least one temperature sensor,
solder bumps arranged between said heat source and said tube and between said temperature sensor and said tube, said solder bumps being soldered to said tube and said heat source or that temperature sensor, respectively, and forming a first thermal connection between said heat source and said tube and a second thermal connection between said temperature sensor and said tube, wherein the thermal connections are located at a distance from each other.
In a final aspect, the invention relates to a semiconductor substrate for a flow sensor, said semiconductor substrate comprising
a flow detector integrated on the substrate, said flow detector having at least one heat source and at least one temperature sensor,
at least one first solder bump arranged on said heat source and
at least one second solder bump arranged on said temperature sensor for attaching said substrate to a tube using flip-chip technique.
The invention relies on the concept of using the xe2x80x9cflip chipxe2x80x9d technique for applying the substrate to the tube. This technique is conventionally used for electrically connecting semiconductor chips to flat substrates, such as printed circuit boards.
For this purpose, solder bumps are applied to the heat source and the temperature sensors(s) and/or to the tube. The substrate is placed against the tube and heat is applied for melting the solder bumps. After cooling, the solder bumps form thermal connections between the heat source and the tube and between the temperature sensor(s) and the tube, respectively.
Preferably, a structure is applied to the tube before placing the substrate against it. This structure provides regions of differing wettability, i.e. that are wetted differently by liquid solder, and it is matched to the positions of the solder bumps. This allows a controlled wetting of the tube surface by the solder bumps. It prevents undesired thermal bridges between the bumps and, due to surface tension forces, helps to align the substrate correctly against the tube.
If the tube has a curved surface, the structure is preferably created by applying a flexible photomask against it.
The invention also relates to a flow sensor that can be produced with this method as well as to a substrate to be used for producing such a flow sensor. The substrate is provided with a first solder bump arranged on the heat source and a second solder bump arranged on the temperature sensor(s) so that the substrate can be applied to a tube using the flip chip technique.